In recent years, in the field of automatic transmissions, efforts have been made to increase the number of gears in order to improve the fuel efficiency. For example, Patent Document 1 discloses an automatic transmission including four planetary gear sets, namely, first to fourth planetary gear sets RS1-RS4, and five frictional engagement elements, namely, brakes A and B, and clutches C, D, and E, to provide eight forward gears and one reverse gear. In this automatic transmission, the brakes A and B, and the clutch C are engaged in a first gear. This allows power from a power source to be input to a sun gear of the third planetary gear set PS3 via an input shaft. Since a ring gear of the third planetary gear set RS3 is fixed, the power is transmitted to a carrier of the third planetary gear set RS3, and is output from this carrier to an output engaged with this carrier.